Method of apparatus for detecting particles on a specimen

ABSTRACT

An apparatus for inspecting a pattern to detect a small pattern defect has an illuminating light source, as illuminating optical system having a plurality of illuminating portions for switching an optical path of illuminating light flux to a surface of board constituting the inspected object from a plurality of directions different from each other, a detecting optical system having a variable magnification using an object lens for condensing reflected diffracted light from the illuminated board, a focusing optical system having a variable magnification capable of focusing an optical image by converged reflected diffracted light with a desired focusing magnification and an optical detector for detecting the optical image focused by the focusing optical system to convert it into an image signal, an A/D converter for converting the image signal into a digital image signal, and an image signal processor for processing the digital image signal to detect the defect.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for detecting aparticle present on a thin film board, a semiconductor board or aphotomask in the process of fabricating a semiconductor chip or a liquidcrystal product. The present invention also relates to a method andapparatus for detecting a defect produced at a circuit pattern andinspecting the situation which may have caused production of a particleor a defect in a step of fabricating a device which is subjected to ameasurement by analyzing the detected particle or defect.

In a step of fabricating a semiconductor device, when a particle ispresent on a semiconductor board (wafer), the particle may constitutethe cause of an insulation failure or a shortcircuit of the wiring.Further, in accordance with the demand for miniaturization of asemiconductor element, a fine particle also constitutes a cause of aninsulation failure of a capacitor or the destruction of a gate oxidefilm. The particles are mixed at various stages due to various causes,and they may be produced from a movable portion of a carrying apparatus,produced from the human body, produced by a reactor in a processingapparatus by a process gas, or mixed with a drug or a material.

Similarly, also in a step of fabricating a liquid crystal displayelement, when a particle is mixed on a pattern or some defect isproduced, the display element cannot be used. The situation stays thesame also in a step of fabricating a printed board, and a shortcircuitof a pattern or a failure in a connection may be caused by such aparticle.

As one of the technique for detecting a particle on a semiconductorboard, JP-A-62-89336 (Patent publication 1), discloses a method ofeffecting a highly sensitive and highly reliable inspection of a productfor a particle or other defect by eliminating false information in apattern by irradiating a laser beam onto a semiconductor board,detecting light scattered from a particle produced when the particle isadhered onto the semiconductor board, and comparing a result ofinspecting a semiconductor board of the same kind that was inspectedimmediately therebefore. Further, JP-A-63-135848 (Patent publication 2)discloses a method which involves irradiating laser light onto asemiconductor board, detecting light scattered from a particle which isadhered on the semiconductor board and analyzing the detected particleby laser photoluminescence or an analyzing technology of secondary X-rayanalysis (XMR).

Further, as a technique for inspecting a wafer to detect the presence ofa particle, there is a method which involves irradiating coherent lightto the wafer, removing light emitted from a repeated pattern on thewafer using a spatial filter and emphasizing the received pattern todetect a particle or a defect which is not provided with repeatability.Further, a particle inspecting apparatus is described in JP-A-1-117024(Patent publication 3) in which a circuit pattern formed on a wafer isirradiated from a direction which is inclined relative to a main groupof linear lines of the circuit pattern by 45 degrees to prevent 0-orderdiffracted light from the main group of linear lines from being incidenton an aperture of an object lens. According to this technique, it isalso proposed to block light from other groups of linear lines, whichare not the main group of linear lines using a spatial filter.

Further, an apparatus and a method of inspecting an object for a defectin the form of a particle or the like is described in, for example,JP-A-8-271437 and JP-A-2000-105203 (Patent publications 4).Particularly, in JP-A-2000-105203, it is proposed to change the size ofa detected pixel by switching the detecting optical system. Further, atechnique for measuring the size of a particle is described in, forexample, JP-A-2001-60607 (Patent publication 5).

However, according to the techniques proposed in the above-citedpublications, consideration is not given to a constitution capable ofdetecting a fine particle or a defect, on a board on which a repeatedpattern are mixed, and a nonrepeated pattern with high sensitivity andat high speed. That is, according to the technologies disclosed in theabove-described publications, consideration is not given to aconstitution capable of achieving a detection sensitivity (minimumdetected particle dimension) equivalent to that of a repeated patterneven at areas other than the repeated pattern portion of, for example, amemory cell portion.

Further, according to the technologies disclosed in the above-describedpublications, consideration is not given to a constitution capable ofpromoting a good sensitivity in detecting a small particle or a defectat the 0.1 μm level in a region having a high pattern density. Further,according to the technologies disclosed in the above-describedpublications, consideration is not given to a constitution capable ofpromoting a good sensitivity in detecting a particle or a defect thatproduces a shortcircuiting of wirings or a good sensitivity in detectinga particle in the shape of a thin film.

Further, according to the technology disclosed in JP-A-2001-60607,consideration is not given to a constitution capable of promoting anincreased accuracy in the measurement of a particle or a defect.

Further, according to the technology disclosed in JP-A-2001-60607,consideration is not given to a constitution capable of promoting a goodsensitivity in detecting a particle on a surface of a wafer formed witha transparent thin film.

SUMMARY OF THE INVENTION

The present invention provides a method of inspecting a defect in theform of a small particle or other defect of the 0.1 μm level for a boardconstituting an inspected object, on which a repeated pattern and anonrepeated pattern are mixed, at high speed and with high accuracy, andit provides an apparatus to perform the method for resolving theabove-described problems.

Further, the invention provides a method of inspecting a product for aparticle or other defect with high sensitivity, even in a region havinga high pattern density, and it provides an apparatus to perform themethod.

Further, the invention provides a method of inspecting a product for aparticle causing shortcircuiting of wirings, such as a defect or aparticle having the shape of a thin film, with a high sensitivity, andit provides an apparatus to perform the method.

That is, according to the present invention, there is provided anapparatus for inspecting a board to detect a defect, comprising anilluminating light source; illuminating optical system means having aplurality of irradiating portions for irradiating an illuminating lightflux emitted from the illuminating light source to a surface of theboard from a plurality of directions that are different from each other,and an optical path switching portion for switching the illuminatingoptical flux among the plurality of illuminating portions; detectingoptical system means having a variable magnification, including anobject lens for condensing reflected diffracted light from the boardilluminated by the illuminating optical system means; a focusing opticalsystem having a variable magnification capable of focusing an opticalimage produced by the reflected diffracted light that has been condensedby the object lens by a desired focusing magnification and an opticaldetector for detecting an optical image focused by the focusing opticalsystem to convert it to an image signal; A/D converting means forconverting the image signal provided from the optical detector of thedetecting optical system means into a digital image signal; and imagesignal processing means for processing the digital image signal that hasbeen converted by the A/D converting means to detect a defect.

Further, according to the invention, a method of inspecting a boardconstituting an inspected object for detecting a defect, comprises thesteps of irradiating an illuminating light flux emitted from anilluminating light source to a surface of the board, by continuouslymoved in one direction, from a skewed direction; detecting an opticalimage produced by reflected diffracted light generated from the board byuse of a sensor; and processing an image signal detected by the sensorto inspect the defect; wherein an optical path of the illuminating lightflux emitted from the illuminating light source is switched inaccordance with the kind of particle defect to irradiate a surface ofthe board constituting the inspected object from different directions,and the enlarging magnification of the optical image produced by thereflected diffracted light from the board is changed in accordance withthe density of a pattern formed at a region on the board constitutingthe inspected object, to thereby detect the defect using the sensor.

According to the invention, it is possible to achieve an effect ofreducing the diffracted light from a circuit pattern on a board of anLSI pattern or the like and of detecting a small particle or defect ofthe 0.1 μm level, a particle or a defect shortcircuiting wirings, or aparticle having the shape of a thin film at high speed and with highaccuracy for a board constituting an inspected object that has atransparent film in the form of an oxide film or the like formed at asurface thereof and on which a repeated pattern and a nonrepeatedpattern are mixed.

These and other objects, features and advantages of the invention willbe apparent from the following more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prospective view showing an embodiment of a particleinspecting apparatus according to the invention;

FIG. 2A is a diagram showing a side view and FIG. 2B is a diagrammaticprospective view of the illuminating optical system shown in FIG. 1;

FIGS. 3A and 3B are diagrams illustrating a function of a conical curvedface lens used in the illuminating optical system;

FIGS. 4A and 4B are diagrams illustrating the operation of making amultiplication variable portion of the detecting optical system shown inFIG. 1 variable;

FIGS. 5A to 5C are diagrams illustrating the function of the eyeobserving optical system shown in FIG. 1;

FIG. 6 is a diagram showing an embodiment of a first detecting opticalsystem according to the invention;

FIGS. 7A and 7B are diagrams showing another embodiment of a detectingoptical system;

FIG. 8A is a diagram which illustrates an illumination portion and FIG.8B is a diagram showing a detecting portion of the detecting opticalsystem shown in FIG. 7;

FIG. 9 is a diagram showing another embodiment of an inspectingapparatus;

FIGS. 10A and 10B are diagrams illustrating another embodiment of anoptical detector;

FIGS. 11A and 11B are diagrams illustrating another embodiment of anoptical detector;

FIG. 12 is a block diagram showing the signal processing system shown inFIG. 1;

FIG. 13 is a diagram illustrating a threshold calculation processingportion; and

FIG. 14 is a block diagram showing an embodiment to which an observingoptical system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An explanation will be given of an embodiment according to the presentinvention with reference to the drawings.

A defect inspecting apparatus according to the invention makes itpossible to inspect a product for a defect, such as a particle on adetected board of a wafer or the like, and for various defects whichconstitute a pattern defect, a micro scratch and the like, in variouskinds of product and various fabricating steps, with high sensitivityand at high speed, particularly to detect a defect on a surface of athin film formed on a surface of a wafer by separating the defect from adefect in the thin film. For that purpose, in a defect inspectingapparatus according to the invention, as shown in FIG. 1, an angle α ofirradiating and a direction φ of irradiating a slit-like beam 201, whichis illuminated by an illuminating optical system 10, are made to bevariable in accordance with the object being inspected, a detectingoptical system 20 is installed to constitute an imaging relationshipwith respect to the surface of the inspected object and a lightreceiving face of a detector 26, and the size of a detected pixel is setin accordance with the size of a detected defect by making themultiplication of the detecting optical system 20 variable, to therebycarry out an inspection.

Further, the defect inspecting apparatus according to the invention isalso provided with a function of classifying the kind of defect byconstituting a characteristic amount by a difference of the scatteredlight provided from a defect by, for example, illuminating light havinga different irradiating angle.

First, a specific explanation will be given of a mode of carrying outthe defect inspecting method according to the embodiment. Further,although in the following mode of carrying out the invention, anexplanation will be given of a case of inspecting a small/large particleor micro scratch on a transparent film formed on a semiconductor waferand a defect of a particle or a pattern defect in the transparent film,the invention is not limited to a semiconductor wafer, but is applicablealso to a thin film board, a photomask, a TFT, a PDP or the like.

As shown FIG. 1, the defect inspecting apparatus according to thisembodiment is provided with a wafer carrying system 30 constituted byXYZ stages 31, 32, 33, 34 for mounting and moving a board 1 constitutingan inspected object in the form of a wafer or the like provided fromvarious product kinds or various fabricating steps and a controller 35;an illuminating optical system 10 for illuminating light emitted from alaser light source 11 onto the board 1 from a plurality of skeweddirections after enlarging the light to a certain size by using a beamenlarging optical system 16, via a lens, a mirror and the like, thedetecting optical system 20 having a variable multiplication constitutedby an object lens 21, a spatial filter 22, a focusing lens 23, anoptical filter group 420 and an optical detector 26 of a TDI imagesensor or the like for detecting reflected diffracted light (orscattered light) from a region illuminated by the illuminating opticalsystem 10; a signal processing system 40 for detecting a particle basedon an image signal detected by the optical detector 26; an observingoptical system 60 illuminating a surface of the wafer 1 by means of anilluminating light source 63, having a lens 61 and image taking means 64for confirming the presence or absence, and a shape of a particledetected by inspection; and a total control portion 50 for settinginspection conditions or the like and controlling a total of theilluminating optical system 10, the inspecting optical system 20 havingthe variable multiplication, the carrying system 30 and the signalprocessing system 40. The total control portion 50 is provided withinputting/outputting means 51 (including also a keyboard or a network),displaying means 52 and a storing portion 53.

Further, the particle inspecting apparatus is provided with an automaticfocusing control system (not illustrated) such that an image on thesurface of the wafer 1 is focused on a light receiving face of theoptical detector 26.

The inspecting apparatus has a constitution that is capable ofilluminating a surface of the board 1 constituting the inspected objectfrom a plurality of directions. As described in Patent publication 5, asshown in FIG. 2A, the illuminating optical system 10 is constituted by abeam enlarging optical system 16 constituted by, for example, a concavelens and a convex lens, not illustrated, for enlarging the light L0emitted from the laser light source 11, a lens 14, a mirror 15 and thelike. As shown in FIG. 2B, the inspecting apparatus of the presentembodiment has a constitution capable of irradiating the slit-like beam201 to the wafer (board constituting inspected object) 1 installed onthe specimen installing base 34 planarly in a plurality of directions(four directions 220, 230, 240, 250 in FIG. 2B) and by a plurality ofilluminating angles.

Here, the illuminating light is constituted by the slit-like beam 201for achieving high speed formation of particle inspection bysummarizingly detecting scattered light from a particle or a defectgenerated by illumination by light receiving elements arranged in onerow. That is, the optical system is constituted such that the slit-likebeam 201 illuminated on the wafer 1 aligned with the chip by beingdirected in a scanning direction of the X stage 31 and a scanningdirection of the Y stage 32 is condensed in the X direction and becomesparallel light in the Y direction, and the optical axis is adjusted tobe orthogonal to the scanning direction X of the X stage 31, in parallelwith the scanning direction Y of the Y stage 32 and also in parallelwith the direction of pixel alignment of the optical detector 26. Theconstitution achieves an effect of being capable of being easilypositioned between chips when an image signal compares between chips.The slit-like beam 201 can be formed by providing, for example, acylindrical lens in an optical path.

In the case of the focusing optical system as shown, for example, inFIG. 4, when the width in the X direction of the slit-like beam 201 ofthe illuminating light is equal to or smaller than the width in a shortaxis direction of the light receiving elements aligned in one rowrelative to the face of the inspection object, the loss of illuminatedlight can be sufficiently reduced. For example, when the width in theshort axis direction of the light receiving element is 200 μm, and themagnification of the focusing optical system is 10 times, theilluminating width may be equal to or smaller than 20 μm. By slenderlynarrowing the illuminating light, the optical energy is concentrated toa local portion of the inspection object to an amount sufficient todamage the inspection object. Therefore, it is important not to narrowthe illumination more than necessary. Hence, in order to avoid damage tothe inspection object, while preventing a loss of the illuminatinglight, it is preferable to constitute the arrangement such that“illuminating width”=“width in short axis direction of light receivingelement”÷“magnification of focusing optical system”.

Here, in illuminating from the directions 220 and 230, it is necessaryto form the slit-like beam 201 on the wafer 1 by irradiating laser lightfrom a direction that is rotated in the Y axis direction of the wafer byan angle φ and is inclined in the X axis direction by an angle α.Therefore, the conical curved face lens 14 shown in FIG. 3A, in whichthe radius of curvature in a longitudinal direction is continuouslybeing changed, is arranged in the optical path, and the slit-like beam201 becomes parallel with the scanning direction of the Y stage.Further, in illuminating from the directions 240 and 250, theillumination comes from a direction which is the same as the directionof the scanning of the stage, and, therefore, the slit-like beam 201 canbe formed by a cylindrical lens, as shown in FIG. 3B.

Further, there is a constitution which is capable of changing theilluminating angle α in accordance with the kind of a particleconstituting an inspection object on the board 1 by switching the mirror15 and a mirror 202, as shown in FIG. 2A, using a mechanism, based onthe instruction received from the total control portion 50. There is aconstitution in which, in any case of the illuminating angle, theslit-like beam 201 includes an illuminating region for covering adirection 203 of alignment of the optical detector 26 and the slit-likebeam 201 coincides with the wafer 1, even for illumination from anydirection.

Thereby, illumination having parallel light in the Y direction and at avicinity of φ=45 degrees can be realized. Particularly, by constitutingthe slit-like beam 201 of parallel light in the Y direction, diffractedlight emitted from a circuit pattern, in which main groups of linearlines are directed in the X direction and the Y direction, is blocked bythe spatial filter 22.

A method of fabricating the conical curved face lens 14 is described inPatent publication 5, and, therefore, an explanation thereof will beomitted.

The slit-like beam 201 is formed on the wafer 1 using a plurality ofilluminating angles to deal with detection of particles of various typesproduced on the surface of the wafer 1. That is, there is constructed aconstitution for detecting particles of an object by detection of apattern defect or a particle having a low height on the board 1constituting the detected object. The illuminating angle α is appliedwith an optical value that is empirically provided, since, when theangle is increased, the amount of reflected diffracted light from thecircuit pattern is increased and the S/N ratio is lowered. As anexample, when it is intended to detect a particle having a low height onthe surface of a wafer, the illuminating angle α is preferably a smallangle, for example, α is set to be 1 degree through about 5 degrees.Further, although the illuminating angle α may be increased when it isintended to detect a particle or a pattern defect between wirings in awiring step, the illuminating angle may be set to be about 45 degreesthrough about 55 degrees, in view of the relationship of the S/N ratioof the pattern and the particle. Further, when there is a correspondingrelationship between a step constituting an object of inspection and thekind of particle to be detected, the illuminating angle is set to bepreviously determined in an inspection recipe. In order to detect theabove-described particle or pattern defect on the surface of waferevenly, the illuminating angle may be set to a middle value of theabove-described angles.

Further, with regard to a state of polarizing illumination, when, forexample, the material of a surface of an inspecting object is atransparent material in the form of an oxide film or the like, Ppolarization illumination is provided with a transmittivity that ishigher than that of S polarization illumination, with the result that itis easy to invade inside of the oxide film. Therefore, by changing thepolarization of illumination, an inspection specified to a surface ofthe oxide film, or an inspection specified to a lower layer of the oxidefilm, can be carried out.

Further, in inspecting the oxide film, by setting a difference in theilluminating angle or the transmittivity by polarization, the scatteringintensity of a defect differs by whether the defect is present on thesurface of the oxide film, is in the oxide film or is a lower layer ofthe oxide film. A characteristic amount of the illuminating angle or theintensity of scattered light from the defect in illuminating theinspecting object when the polarization condition is changed, can beeffective in classifying whether the defect is present on the surface ofthe oxide film.

Further, with regard to the illuminating direction φ, for example, inthe case of a wiring step, by aligning a wiring pattern formed on thewafer and the illuminating direction, a particle between the wiringsbecomes easy to detect. Further, when the circuit pattern of the waferis not a wiring pattern, but is a contact hole, a capacitor or the like,there is no specific directionality, and, therefore, it is preferable toilluminate the chip from a direction in the vicinity of 45 degrees.Further, in changing the illuminating angle, the illuminating angle maybe changed by switching two mirrors having different angles, as shown inFIG. 2A, or the angle of a single mirror may be changed using rotatingmeans, not illustrated.

Next, a method of changing the illuminating direction will be explained.A branching optical element 218, as shown in FIG. 2B, is constituted bya mirror, a prism or the like for transmitting or reflecting laser lightL0 emitted from the laser light source 11 to guide it in threedirections by moving the position thereof in the Y direction. Laserlight L1 transmitted through the branch optical element 218 is branchedto from transmitted light and reflected light by a half prism 221, forexample, and the transmitted light is reflected by a mirror 235 againvia a mirror 231, a beam diameter correcting optical system 232, amirror 233, and a conical curved face lens 234 to form the slit-likebeam 201 on the wafer 1 from the direction 230.

Meanwhile, the reflected light at the half prism 221 forms the slit-likebeam 201 on the wafer 1 from the direction 220 by way of an optical pathhaving the same function. Further, beam diameter correcting opticalsystems 222 and 232 adjust the beam diameter of the laser light incidenton the conical curved face lens 14, such that the slit-like beam 201irradiated to the wafer 1 is constituted to have the same size. Further,when a mirror 260 is installed in place of the half prism 235, the beamcan be irradiated only from the direction 220 or the direction 230.Further, by inserting wavelength plates 226, 236 on the rear side of thehalf prism 235, the polarization direction of the irradiated laser beamalso can be aligned.

Meanwhile, laser light L2 reflected by the branch optical element 218transmits through the beam diameter correcting optical 241, thereafter,is reflected by mirrors 242 and 243, transmits through a cylindricallens 244, is reflected by a mirror 245 again and forms the slit-likebeam 201 on the wafer 1 from the direction 240. Laser light L3 forms theslit-like beam 201 on the wafer 1 from the direction 250 by way of anoptical path having the same function.

With regard to the illuminating directions 240 and 250, when a largenumber of wiring patterns formed on the wafer become parallel with the Xdirection in, for example, a wiring step, the direction of illuminationcan be aligned, and an effect of facilitating the detection of aparticle between wirings is achieved.

Further, as the laser light source 11, although a high power laserhaving a wavelength of 532 nm of a YAG second harmonic is used, it isnot necessary that the wavelength is 532 nm, but the laser may be anultraviolet, a far ultraviolet, or a vacuum ultraviolet optical laser,or the light source may be a light source in the form of an Ar laser, anitrogen laser, a He—Cd laser, an excimer laser, or a semiconductorlaser. Generally, by making the laser wavelength short, the resolutionof a detected image is promoted, and, therefore, a highly sensitiveinspection can be carried out. For example, when the NA of the objectlens 21 is about 0.4 in a case of the wavelength of about 0.34 μm andthe NA of the object lens 21 is about 0.2 in the case of a wavelength of0.17 μm, the incidence of diffracted light to the object lens 21 isincreased and the detecting sensitivity can be promoted. Further, withregard to the use of a semiconductor laser or the like, a small-sizedand a low cost apparatus can be realized.

Further, depending on the kind of defect to be detected, the surfaceshape or the material of an inspecting object, there is a case ofpromoting the contrast of a defect in a specific wavelength range ofillumination. Hence, when a preference is given to a number of kinds ofdefects, a usable constitution may be obtained by selecting or mixing aplurality of illumination wavelengths.

Further, as a system for oscillating the laser, there is a continuousoscillation system or a pulse oscillation system. In the case of a pulseoscillation system, the output is dispersed for each pulse, and,therefore, it is preferable to be able to irradiate from 10 pulses toabout several tens of pulses or more in acquiring data of one pixel inthe scanning direction in a detected image.

Next, an explanation will be given of the detecting optical system 20shown in FIG. 4A. The detecting optical system 20 is constituted todetect light that is illuminated by the illuminating optical system 10and then is reflected and diffracted from the board 1 constituting thedetected object of a wafer or the like by the optical detector 26 of aTDI image sensor or the like via the object lens 21, the spatial filter22, the focusing lens (variable magnification focusing optical system)23, and an optical filter group 25 comprising a concentration filter, apolarizer, or the like.

The spatial filter 22 is provided with a function of blocking a Fouriertransformed image by reflected diffracted light from a repeated patternon the wafer 1 and transmitting scattered light from the particle, andit is arranged at a spatial frequency region of the reflecting lens 21,that is, a focusing position of Fourier transformation (incorrespondence with the emitting eye). An eye observing optical system70 comprises a mirror 90 installed in an optical path of the detectingoptical system 20 and having a constitution capable of escaping in the Xdirection in inspection, a projecting lens 91, and a TV camera 92 fortaking a reflected diffracted optical image 501 from a repeated patternat the focusing position of Fourier transformation, as shown in FIG. 5A.

Here, as shown in FIG. 5B, the spatial filter 22 is provided with aconstitution in which a plurality of light blocking portions 503 havinga rectangular shape are aligned at variable intervals p, and it isprovided at the focusing position of Fourier transformation and isconstituted to change the interval p of the light blocking portion 503by a mechanism, not illustrated, in accordance with the reflecteddiffracted optical image 501 from the repeated pattern at the focusingposition of Fourier transformation taken by the TV camera 92. Thereby,as shown in FIG. 5C, when observed by the eye observing optical system70, at the focusing position of Fourier transformation, the image can beadjusted to constitute an image 504 without a bright spot by thereflected diffracted optical image from the pattern. The operation canbe executed based on the instruction of the total control portion 50 byprocessing a signal from the TV camera 92 using the signal processingsystem 40. Further, a light blocking pattern in accordance with thereflected diffracted optical image 501 may be formed based on the signalfrom the TV camera 92, not by the light blocking plate 503, but byusing, for example, a liquid crystal board. Further, a plurality oflight blocking patterns may be prepared and an optimum pattern may beselected for use based on the signal from the TV camera 92.

Further, the spatial filter 22 is also provided with a function ofdealing with two or more repeated pitches in order to block diffractedlight from patterns having different repeated pitches as in, forexample, a memory cell portion and a direct peripheral circuit portion.For example, by arranging a second spatial filter that is shifted byseveral mm in the Z direction relative to the spatial filter in a linearshape, as shown in FIG. 5B, diffracted light of a plurality of patternshaving different pitches can be blocked, and the number of regionscapable of being inspected at a high sensitivity with a one timeinspection can be increased. The second spatial filter may be disposedin parallel with the first spatial filter or it may be orthogonalthereto.

The inspecting apparatus is provided with a function of executing aninspection to detect the presence of a particle at high speed and withthe function of executing an inspection at low speed, while maintaininga high sensitivity. That is, in the case of a detected object ordetecting region in which the circuit pattern is fabricated with a highdensity, by increasing the magnification of the detecting opticalsystem, although the inspecting speed is retarded, an image signal witha high resolution can be provided, and, therefore, a highly sensitiveinspection can be executed. Further, in the case of a detected object oran inspecting region in which the circuit pattern is fabricated with alow density, by reducing the magnification, high speed inspection can berealized while maintaining a high sensitivity. Thereby, the size of aparticle to be detected and the size of the detecting pixel can beoptimized, and it is also possible to efficiently detect only scatteredlight from a particle by excluding noise from other than a particle.

An explanation will be given of the operation of making themagnification of the detecting optical system variable with reference toFIG. 4B. The magnification of the detecting optical system is changedbased on an instruction received from the total control portion 50. Thefocusing lens 23 is constituted by movable lenses 401, 402, a fixed lens403 and a moving mechanism 404 to achieve a characteristic in which itis possible to make the magnification of a surface of a wafer focused onthe detector variable without changing the positions of the object lens21 and the spatial filter 22 in the Z direction in changing themagnification. That is, it is not necessary to change the relativepositions of the board 1 constituting the detected object and theoptical detector 26 even when changing the magnification, and themagnification can be changed by a simple constitution of the drivemechanism 404. Further, the size of a Fourier transformation face is notchanged, and, therefore, an advantage is attained in that the spatialfilter 22 need not be changed.

The magnification M of the detecting optical system 20 is characterizedby the following Equation (1) in which the focal length 405 of theobject lens 21 is designated by notation f₁ and the focal length 406 ofthe focusing lens 23 is designated by notation f₂.M=f ₁ /f ₂   (1)Therefore, in order to set the variable magnification of the detectingoptical system 20 to the magnification M, since f₁ is a fixed value, thesystem is moved to a position in which f₂ becomes (f₁/M). That is, inthe inspecting apparatus, the magnification of the detecting opticalsystem 20, which is arranged upward from a position where the wafer 1 isinstalled, is made to be variable by a simple constitution.

Next, the details of the moving mechanism 404 will be explained withreference to FIG. 4B. FIG. 4B shows the constitution used for moving themovable lenses 401 and 402 to specific locations. The movable lens 401is held by a lens holding portion 410 and the movable lens 402 is heldby a lens holding portion 420. The lens holding portion 410 and the lensholding portion 420 are moved to predetermined positions in the Zdirection independently from each other by rotating a ball screw 412using a motor 411 and by rotating a ball screw 422 using a motor 421.

A movable portion 415 or 425 of a positioning sensor is provided at afront end of the lens holding portion 410 or 420, which serves to holdthe movable lens 401 or 402. The detecting portion 416 or 426 of thepositioning sensor is provided at a position where the movable lens 401or 402 is to be stopped. The lens holding portion is moved in the Zdirection by driving the motor 411 or 421, and the positioning sensor416 or 426, provided installing at a position of a desiredmagnification, detects the positioning sensor movable portion 415 or 425to position the lenses. Further, a positioning sensor 440 serves to alimit sensor establishing an upper limit in the Z direction, and apositioning sensor 430 serves to a limit sensor establishing a lowerlimit in the Z direction. Here, an optical or a magnetic sensor isconceivable for use as the positioning sensor.

The operation is executed based on an instruction received from thetotal control portion 50, and the magnification is set in accordancewith the pattern density of the board 1 constituting the inspectedobject which is mounted on a stage. For example, when a circuit patternis formed with a high density, an inspection mode having a highsensitivity is constituted by selecting a high magnification; and, whenthe circuit pattern is formed with a low density, or when high speedinspection is needed, a low magnification is selected.

Further, it is also conceivable to unitize the movable lens portion andreplace the magnification variable means with such a unit when themagnification is not changed frequently. In this case, there is anadvantage of easily executing adjustment and maintenance.

Meanwhile, as described above, the illuminating angle is determined bythe type of particle to be detected on an inspected object, and theilluminating angle and the illuminating direction of the illuminatingoptical system 10 are changed, in accordance with the board 1constituting the inspected object mounted on a stage, based on aninstruction received from the total control portion 50.

Meanwhile, in inspecting a product for a particle, it is necessary toalso have the ability to inspect a multilayer wafer, the use of whichhas tended to increase in recent years due to high integration ofsemiconductor devices. A transparent film (for example, oxide film) isformed on a surface of the wafer in a step of forming multilayers, and amultilayer wafer is produced by repeating a step of forming a patternthereon. There is an enhanced need for detecting only a particle on asurface of an oxide film in inspecting a wafer formed with an oxidefilm. Although, basically, it is possible to restrain the influence ofreflected light from a matrix of pattern diffracted light or the like byreducing the illuminating angle α, there is a problem in that, byreducing the illuminating angle α, scattered light emitted from aparticle on a side of regular reflection of illuminated light, that is,front scattered light, is increased, the incidence of scattered light onthe detecting optical system provided above becomes small and theparticle cannot be detected stably.

Hence, according to the embodiment, as shown in FIG. 6, laser light L3,the beam diameter of which is enlarged is illuminated onto the wafer 1by an illuminating angle γ relative to the surface of the wafer via amirror 610 and a condensing lens 620 to thereby form slit-like beam 601.A detecting optical system comprising a focusing lens 630 and a detector640 is arranged in a direction 260, which substantially orthogonallyintersects with the illuminating direction 250, and in a direction of ahorizontal angle φ and a detecting angle θ, to thereby detect sidescattered light from a particle present on the surface of the thin filmthat has been emitted by the slit-like beam 601 illuminated onto thethin film formed on the surface of the wafer. The light receiving faceof the detector 640 is arranged at a position representing an imagingrelationship with the slit-like beam 601 via the focusing lens 630, andthe focusing lens 630 is set with a focusing magnification such that thelight receiving face of the detector faces the total illuminating rangeof the slit-like beam 601. By causing the detecting system to have thisimaging relationship, the influence of stray light from other than thedetecting object can be prevented, further, parallel processing can beexecuted by outputting signals in parallel from a plurality of pixelsconstituting the sensor, and, therefore, there is the advantage ofachieving a high speed formation of inspection. In the inspection, thelight receiving face of the detector is controlled such that the totalilluminating range of the slit-like beam 601 is caught by an automaticfocusing control system, not illustrated, such that the surface of thewafer is disposed at a constant position in the Z direction. Here, asthe detector, a TDI sensor or a one-dimensional or two-dimensional imagesensor is used. Further, it is also possible to block reflecteddiffracted light from a pattern by installing a spatial filter in thelight path.

As the illuminating direction, the detected object may be illuminatedfrom the direction 220 or the direction 230. However, when the detectingoptical system comprising the focusing lens 630 and the detector 640 isarranged in the direction 260, the system is constituted to illuminatefrom the direction 220. In illumination from the direction 230, thedetecting optical system comprising the focusing lens 630 and thedetector 640 is arranged at a position on a side opposed to the focusinglens 630 and the detector 640 by constituting an axis of symmetry on theY axis, also it is necessary to arrange the system at a position whichdoes not interfere with the illuminating system arranged in thedirection 230. Further, when detection is effected at a position on theside opposed to the focusing lens 630 and the detector 640 byinterposing the Y axis by illuminating from the direction 230, it ispreferable to set the detecting angle θ such that illuminating lightfrom the direction 230 does not reach the detector 640. Thereby, aparticle on the wafer can be accurately detected only by restraining theinfluence of reflected light from a matrix, such as pattern diffractedlight or the like.

Further, as shown in FIG. 7A, for example, laser light L3 may beilluminated by being scanned at high speed in the Y direction bydeflecting means 730, and scattered light from a particle may be guidedby distributing means 750, in the form of an optical fiber or the like,and detected by photoelectric conversion elements 760 a through 760 d,in the form of photomultipliers or the like. In this case, high speedformation of inspection is achieved by forming a group of a plurality ofscanning spots on a wafer, as shown in FIG. 7B. Further, in detectingscattered light from a particle emitted from respective scanning spots701 a through 701 d, as shown in FIG. 8A, the deviation of detection canbe reduced by providing a constitution capable of picking up lightinformation guided by the distributing means 750 at constant aligningintervals to be detected by the photomultipliers.

Further, as shown in FIG. 8B, the plurality of scanning spots areconstituted by dividing laser light L3 into a plurality of beams usingbranching means 710 and the respective spots are scanned in Y directionat the wafer by deflecting means 720. In this case, respectivepolarizers 725 a through 725 d modulate the respective light beams usingfrequencies that are different from each other. The respectivephotomultipliers 760 a through 760 d receive scattered light by scanningthe respective spots and detecting scattered light from a particleemitted by scanning a specific spot by using a circuit, not illustrated,detecting electric signals outputted from the respectivephotomultipliers. Further, inspection can be constituted by high speedformation also by installing a plurality of detecting heads unitizedwith a laser illuminating system and a detecting system in a directionof alignment of the chip 1202, as shown in FIG. 7B, preferably, inconformity with the pitch of the chip, as shown in FIG. 9, instead ofscanning the plurality of laser spots.

An ND filter 24, arranged at the detecting optical system 20, is usedfor adjusting the amount of light detected by the optical detector 26,and, when reflected light having a high brightness is received by theoptical detector 26, the optical detector 26 is brought into a saturatedstate and cannot detect a particle stably. Although the ND filter 24 isnot necessarily needed when the amount of illuminating light can beadjusted by the illuminating optical system portion 10, by using the NDfilter 24, the width at which the amount of detected light is adjustedcan be increased, and the light amount can be adjusted so as to beoptimized for various inspected objects. For example, by combining thelaser light source 11, so that the output is capable of being adjustedfrom 1 W through 100 W with ND filters in the form of a 100%transmission filter and a 1% transmission filter, the light amount canbe adjusted from 10 mW to 100 W, and the light amount can be adjusted ina wide range.

The optical filter 25 is, for example, a polarizing element. Thepolarizing element is used for blocking a component of polarized lightby reflected diffracted light emitted from an edge of a circuit patternwhen illuminating polarized light by means of the illuminating opticalsystem portion 10 and transmitting a portion of the component ofpolarized light by reflected diffracted light emitted from the particle,and it is not necessarily needed according to the embodiment.

The optical detector 26 is an image sensor for receiving reflecteddiffracted light condensed by the condensing lens 23 so as to subject itto photoelectric conversion, and it may be provided in the form of a TVcamera, a CCD linear sensor, a TDI sensor, an antiblooming TDI sensor ora photomultiplier.

Here, as a method of selecting the optical detector 26, in the case ofan inexpensive inspecting apparatus, a TV camera or a CCD linear sensoris preferable; and, when weak light is detected with high sensitivity,for example, when a very small particle equal to or smaller than about0.1 μm is to be detected, a sensor or a photomultiplier having afunction of TDI (Time Delay Integration) is preferable.

The intensity of reflected diffracted light from a pattern differsaccording to the region of an inspecting object on a wafer. That is, ata memory cell portion formed with a repeated pattern and having aperipheral portion, the intensity of reflected diffracted light fromother than a particle on the surface of the wafer is more intensified atthe peripheral portion.

Therefore, when the dynamic range of light received by the opticaldetector 26 is large (when light for saturating a sensor is incidentthereon), a sensor having an antiblooming function is preferable, and,as shown in FIG. 10A, a beam splitter having different transmittancesand reflectances may be arranged at an optical path of the detectingoptical system, and a detector may be installed at each optical path. Inthis case, even when strong light saturating one sensor 1026 is incidentthereon, another sensor 1027 detects light having an attenuated lightamount, and, therefore, a particle can be detected. Further, in the caseof using a TDI sensor, as shown in FIG. 10B, it is also conceivable touse an element formed with a light receiving portion having a differentnumber of stages for picking up a signal in an array of light receivingelements of, for example, 100 stages. For example, by dividing a portionof the pick up signal of 1 stage of an array of light receiving elementsand a portion of the pick up signal from the remaining 99 stages, evenin the case of incidence of strong light, and even when blooming isbrought about at the portion where the signal of 99 stages is picked up,the blooming can be prevented at the portion where the signal of 1 stageof the array of light receiving elements is picked up, and respectiveoutput signals may be processed in the signal processing system 40.

Further, even when the diffracted light from the memory cell portion anda peripheral portion are simultaneously blocked by the spatial filter 20in correspondence with a plurality of pattern pitches, the memory cellportion and the peripheral portion can be inspected with highsensitivity.

Further, when a photomultiplier is used, as shown in FIG. 11, a sensoraligned with the photomultipliers in a one-dimensional direction may beused. In this case, the sensor can be used as a highly sensitiveone-dimensional sensor, and a highly sensitive inspection can be carriedout. In this case, as shown in FIG. 11A, there may be a constitution forattaching a microlens 5002 to a side of the focusing lens 23 of aphotomultiplier 5001 for detecting reflected diffracted light condensedby the focusing lens 23. Here, the microlens 5002 is provided with afunction of condensing light, in a range equivalent to that of the faceof the photomultiplier, to the photomultiplier 5001. Further, as shownin FIG. 11B, there may be a constitution for attaching an optical fiber5004 via a jig 5003 installed downstream from the microlens 5002 and forattaching the photomultiplier 5001 at an output end of the optical fiber5004. In this case, since the diameter of the optical fiber is smallerthan the diameter of the photomultiplier, the sensor pitch can be madesmaller than that of FIG. 11A, and, therefore, a sensor having a highresolution can be constituted.

Further, when a sensor aligned with a photomultiplier is used, in orderto deal with the problem of aging deterioration of the sensor, areference wafer for calibrating the sensitivity of an inspectingapparatus may be used. The inspecting apparatus can stably be operatedby periodically inspecting the wafer for calibrating the sensitivity,thereby establishing a sensitivity for each photomultiplier based on adetecting signal at this occasion.

Next, the carrying system 30 will be explained. The stages 31, 32 arestages that are used for moving the specimen installing base 34 in theXY plane and are provided with strokes capable of moving a total face ofthe board 1 constituting the detected object to an illuminating area ofthe illuminating optical system 10. Further, the stage 33 is a Z stageand is provided with a function of moving the specimen installing base34 in an optical axis direction (Z direction) of the detecting opticalsystem 20. Further, the specimen installing base 34 is provided with afunction of holding the wafer 1 by means of vacuum adsorption or thelike and rotating the board 1 constituting the detected object in aplane. Further, the stage controller 35 is provided with a function ofcontrolling the stages 31, 32, 33 and the specimen installing base 34.

Next, an explanation will be given of the signal processing system 40,which is used for processing an output signal from the optical detector26 for receiving reflected diffracted light from the surface of thewafer 1 to subject it to photoelectric conversion, with reference toFIG. 12. The signal processing system 40 is constituted by an AIDconverter 1301; a data storing portion 1302 for storing a detected imagesignal f (i, j) that has been subjected to A/D conversion; a thresholdcalculation processing portion 1303 for effecting a processing tocalculate a threshold based on the detected image signal, particledetection processing portions 1304 a through 1304 n for effecting aprocessing to detect a particle for respective pixel images, based on adetected image signal 410 provided from the data storing portion 1302and a threshold image signal (Th (H), Th (Hm), Th (Lm), Th (L)) 420provided from the threshold calculation processing portion 1303; acharacteristic amount calculating circuit 1310 for calculating acharacteristic amount of scattered light provided by detecting a defectby low angle illumination, an amount of scattered light provided bydetecting a defect by high angle illumination, a number of detectedpixels showing a width of a defect or the like; an integral processingportion 1309 for classifying various defects of a small/large particle,a pattern defect, a micro scratch and the like on the semiconductorwafer; and a result display portion 1311. Respective ones of theparticle detection processing portions 1304 a through 1304 n areconstituted by pixel merge circuit portions 1305 a through 1305 n, 1306a through 1306 n, particle detection processing circuits 1307 a through1307 n, and inspection region processing portions 1308 a through 1308 nin correspondence with respective ones of merge operators of, forexample, 1×1, 3×3, 5×5, . . . n×n.

Particularly, the embodiment is characterized by the particle detectionprocessing portions 1304 a through 1304 n, the characteristic amountcalculating circuit 1310, and the integrally processing portion 1309.

Next, the operation of the signal processing system 40 will beexplained. First, a signal provided by the optical detector 26 isdigitized by the A/D converter 1301. The detected image signal f (i, j)410 is held in the data storing portion 1302 and is also transmitted tothe threshold calculation processing portion 1303. A threshold image Th(i, j) 420 is calculated for detecting a particle by the thresholdcalculation processing portion 1303, and a particle is detected by theparticle detection processing circuit 1307 based on a signal processedby the pixel merge circuits 1305, 1306. The detected particle signal andthe threshold image are subjected to a processing for a detectedlocation by the inspection region processing portion 1308.Simultaneously, a characteristic amount (for example, an amount ofscattered light provided by high angle illumination, an amount ofscattered light provided by low angle illumination, a number of detectedpixels of a defect or the like) is calculated by the characteristicamount calculating circuit 1309, based on signals provided from thepixel merge circuits 1305 a through 1305 n, 1306 a through 1306 n, theparticle detection processing circuits 1307 a through 1307 n, and theinspection region processing portions 1308 a through 1308 n of theparticle detection processing portions 1304 a through 1304 n providedfor respective merge operators. The particle signal and thecharacteristic amount are integrated at the integral processing portion1309, and an inspection result is displayed at the result displayportion 1311.

Details thereof will be described as follows. First, the A/D converter1301 is a circuit having a function of converting an analog signalprovided by the optical detector 26 into a digital signal, and theconversion bit number is preferably from 8 bits to about 12 bits. Thisis because, when the bit number is small, the resolution of the signalprocessing becomes low, and it is difficult to detect a small amount oflight, whereas, when the bit number is large, there is a disadvantage inthat the A/D converter becomes expensive and the price of the apparatusbecomes high. The data storing portion 1302 is a circuit for storing adigital signal that has been subjected to A/D conversion.

Next, the pixel merge circuit portions 1305, 1306 will be explained withreference to FIG. 10. The pixel merge circuit portions 1305 a through1305 n, 1306 a through 1306 n are constituted by merge operators 1504that are different from each other. The merge operator 1504 is afunction of coupling respective ones of the detected image signal f (i,j) 410 provided from the data storing portion 1302 and the differencethreshold image signal 420, comprising a detected threshold image Th(H), a detected threshold image Th (L), a detected threshold image Th(Hm) and a detected threshold image Th (Lm), provided from the thresholdcalculation processing portion 1303 in a range of n×n pixels, and it is,for example, a circuit for outputting an average value of n×n pixels.Here, the pixel merge circuit portions 1305 a, 1306 a are constituted bymerge operators for merging, for example, 1×1 pixels, the pixel mergecircuit portions 1305 b, 1306 b are constituted by merge operators formerging, for example, 3×3 pixels, the pixel merge circuit portions 1305c, 1306 c are constituted by merge operators for merging, for example,5×5 pixels, . . . the pixel merge circuit portions 1305 n, 1306 n areconstituted by merge operators for merging, for example, n×n pixels. Themerge operator for merging 1×1 pixels outputs the input signals 410, 420as they are.

Further, the influence of vibration of the stage or the like can bereduced by positioning images of image data used for forming thethreshold, such as those of dies contiguous to each other, beforeexecuting the merge processing.

As described above, the threshold image signal comprises four imagesignals (Th (H), Th (Hm), Th (Lm), Th (L)), and, therefore, four mergeoperators Op are needed in each of the pixel merge circuit portions 1306a through 1306 n. Therefore, detected image signals are outputted fromthe respective pixel merge circuit portions 1305 a through 1305 n asdetected image signals 431 a through 431 n that are subjected to mergeprocessing by the various merge operators 1504. On the other hand, thefour threshold image signals (Th (H), Th (Hm), Th (Lm), Th (L)) aresubjected to merge processing by the various merge operators Op1 throughOpn and are outputted as the threshold image signals 441 a (441 a 1through 441 a 4) through 441 n (441 n 1 through 441 n 4) from therespective pixel merge circuit portions 1306 a through 1306 n. Further,the merge operators in the respective pixel merge circuit portions 1306a through 1306 n are the same.

The effect of merging a pixel will be explained here. According to theparticle detecting apparatus of this embodiment, it is necessary todetect not only a small particle, but also a large particle in the shapeof a thin film widened in a range of several μm without oversight.However, a detected image signal from the particle in the shape of athin film is not necessarily enlarged, and, therefore, the SN ratio islow in a detected image signal by a unit of one pixel and oversight maybe brought about. Hence, when the level of a detected image signalaveraged by one pixel is designated by notation S, and an averagedispersion is designated by σ/n, by cutting out the image by a unit ofn×n pixels in correspondence with the size of the particle in the shapeof a thin film to subject it to a convolution operation, the level ofthe detected image signal becomes n²×S and the dispersion (N) becomesn×σ. Therefore, the SN ratio becomes n×S/σ. On the other hand, when theparticle in the shape of a thin film is going to be detected by the unitof one pixel, the level of the detected image signal becomes S, thedispersion becomes σ and, therefore, the SN ratio becomes S/σ.Therefore, the SN ratio can be increased by n times by cutting out theimage by the unit of n×n pixels in correspondence with the size of aparticle having the shape of a thin film to subject it to a convolutionoperation.

With regard to a small particle of about a unit of one pixel, the levelof the detected image signal detected by the unit of one pixel becomesS, the dispersion becomes σ, and, therefore, the SN ratio becomes S/σ.When it is assumed that, the image is cut out by a unit of n×n pixelsfor a small particle of about the unit of one pixel to subject it to aconvolution operation, the level of the detected image signal becomesS/n², the dispersion becomes n×σ and, therefore, the SN ratio becomesS/n³/σ. Therefore, with regard to a small particle of about the unit ofone pixel, the SN ratio can be increased by the signal of the unit of apixel as it is.

Further, according to this embodiment, although an explanation has beengiven using an example in which the range of merging in a square shape(n×n pixels) has been employed, the range of merging may be constitutedby a rectangular shape (n×m pixels). In this case, the range of mergingof the rectangular shape is effective when a particle having adirectionality is detected or, although a pixel detected by the opticaldetector 26 is rectangular, when the signal processing is intended toinvolve processing by a pixel in a square shape.

Further, although the function of the merge operator in this embodimenthas been explained by reference to an example of outputting an averagevalue of n×n pixels, a maximum value or a minimum value or a centralvalue of n×n pixels may be outputted. When the central value is used, astable signal is provided. Further, the average value of n×n pixelsmultiplied by or divided by a specific value may be constituted as anoutput value.

Next, the inspection region processing portions 1308 a through 1308 nwill be explained. The inspection region processing portions 1308 athrough 1308 n are used when the data of a region (including a region inthe chip) which is not necessary for inspection is removed from a signalof a particle in the form of a defect provided by specifying the chipfrom the particle inspection processing circuits 1307 a through 1307 n,when the detection sensitivity is changed for respective regions(including a region in the chip), and when a region intended to beinspected is conversely selected. When, for example, the detectionsensitivity may be low at a region on the board 1 constituting theinspected object, the inspection region processing portions 1308 athrough 1308 n may set a threshold of the region provided from thethreshold calculating portion 1411 of the threshold calculationprocessing portion 1303 to be high, or there may be constituted a methodof leaving only data of a particle of a region to be inspected based oncoordinates of the particle obtained from data of particles outputtedfrom the particle detection processing circuits 1307 a through 1307 n.

Here, a region at which the detection sensitivity may be low is, forexample, a region where the density of a circuit pattern is low in theboard 1 constituting the detected object. An advantage of lowering thedetection sensitivity resides in an efficient reduction in the number ofpieces of detection. That is, in an inspecting apparatus having a highsensitivity, there is a case of detecting several tens of thousands ofparticles. In this case, what is truly important is a particle of aregion at which a circuit pattern is present, and it is a shortcut todeal with the important particle for increasing the yield in fabricatinga device. However, when the total region on the board 1 constituting thedetected object is inspected using the same sensitivity, since animportant particle and an unimportant particle are mixed, the importantparticle cannot be easily sampled. Hence, in the inspection regionprocessing portions 1308 a through 1308 n, by lowering the detectionsensitivity of a region on which a circuit pattern is not present andwhich does not significantly influence the yield based on CADinformation or threshold map information in the chip, the importantparticle can be efficiently sampled. However, the method of sampling theparticle is not limited to a changing of the detection sensitivity, butthe important particle may be sampled by classifying the particles, aswill be mentioned later, or the important particle may be sampled basedon the size of the particle.

Next, the integral processing portion 1309 and the inspection resultdisplay portion 1311 will be explained. The integral processing portion1309 is provided with a function of integrating a result of detecting aparticle that is subjected to parallel processing by the image mergecircuits 1305, 1306, integrating the characteristic amount calculated bythe characteristic amount calculating circuit 1310 and the particledetecting result and transmitting the result to the result displayportion 1311. It is preferable to execute the inspection result integralprocessing by use of a PC or the like to facilitate a change to theprocessing content.

First, the characteristic amount calculating circuit 1310 will beexplained. The characteristic amount is a value representing acharacteristic of a detected particle or defect, and the characteristicamount calculating circuit 1310 is a processing circuit for calculatingthe characteristic amount. As the characteristic amount, there are, forexample, the amount of reflected diffracted light (amount of scatteredlight) (Dh, D1) from a particle or a defect provided by high angleillumination and low angle illumination, the number of detected pixels,the shape and direction of an inertia main axis of a region fordetecting a particle, the location of the detection of a particle on awafer, the kind of circuit pattern of a matrix, and the threshold usedin detecting a particle.

FIG. 14 shows an embodiment of a defect inspecting apparatus with anattached microscope. According to the embodiment, there is aconstitution capable of confirming a particle detected by inspection byuse of the observing optical system 60. The observing optical system 60observes an image by moving a detected particle (including falseinformation) on the wafer 1 to a position of a field of view of themicroscope of the observing optical system 60 by moving the stages 31,32.

An advantage of providing the observing optical system 60 resides in thefact that the detected particle can be observed at once without movingthe wafer to a review apparatus of the SEM or the like. By observing thedetected object at once by use of the inspecting apparatus, the cause ofproducing the particle can be specified swiftly.

Further, an image of the TV camera 64 of the observing optical system 60is also provided with a function of displaying a detected particle on acolor monitor commonly used by a personal computer. The system iscapable of partially irradiating a laser, and executing inspection byscanning the stages centering on coordinates of the detected particleand marking an image of scattered light of the particle and the positionof the particle to display this information on the monitor. Thereby, itcan be confirmed whether a particle actually has been detected. Further,a partial image obtained by scanning the stages can acquire also animage for inspecting a die contiguous to a die at which the particle isdetected, and, therefore, comparing and confirming can be executed atthe location.

Further, the observing optical system 60 may be a microscopeconstituting a light source producing visible light (for example, whitelight) or a light source producing ultraviolet light. Particularly, inorder to observe a small particle of the 0.1 μm level, a microscopehaving a high resolution, for example, a microscope using ultravioletlight, is preferable. Further, when a microscope employing visible lightis used, there is an advantage of providing color information of aparticle, thereby making it possible to easily recognize a particle.

Further, since transmittance differs according to the wavelength of thelight source depending on the material of the surface of an inspectingobject, there is a case in which it is difficult to confirm a defectusing a light source in a wave length band different from theilluminating wavelength used in inspection. Therefore, there may be aconstitution that is capable of selecting a light source in a bandproximate to an inspecting wavelength.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

1. A method of detecting a defect by inspecting a specimen including thesteps of: illuminating a surface of a specimen on which plural patternsare formed and is continuously moved in one direction with a light fluxformed in a shape prolonged in one direction from one of pluralpredetermined directions which are different in elevation angle from oneanother by switching an optical path of the light flux emitted from anilluminating light source in accordance with a kind of defect to bedetected; capturing plural optical images of the specimen illuminated bythe light flux formed in the shape prolonged in one direction withplural image sensors installed in different elevation angle directionsfrom one another by changing an enlarging magnification in accordancewith a density of the pattern formed on the sample in an area irradiatedwith the illuminating light flux formed in the shape prolonged in onedirection; and detecting a defect on the specimen by processing theimages captured by the plural image sensors.
 2. The method according toclaim 1, wherein each of the image sensors installed in the differentelevation angle directions detects image signal of the pattern byblocking a diffracted light pattern formed by diffracted light from arepeated pattern portion of the plural patterns formed on the specimen.3. An apparatus for inspecting a defect on a specimen comprising: anilluminating light source; illuminating optical means having a pluralityof illuminators installed in different elevation angle directions fromone another for illuminating light flux emitted from the illuminatinglight source to a surface of the specimen from a plurality of elevatingangle directions different from each other and an optical path switchingportion for switching the illuminating light flux among the plurality ofilluminators for illuminating light formed substantially in a linearshape to the same location on the specimen; detecting optical meanshaving a plurality of detectors installed in different elevation angledirections from one another for detecting an image of the sampleilluminated by the illuminating optical means in which an enlargingmagnification of the image is variable; and image signal processingmeans for processing an image signal provided by detecting by thedetecting optical means to detect the defect on the specimen.
 4. Theapparatus according to claim 3, wherein the detecting means includes avertical direction detecting optical unit for detecting an image bylight scattered in a perpendicular direction of the surface of thesample, and an obligue direction detecting optical system portion fordetecting an image by light scattered in a direction inclined to thesurface of the specimen.
 5. The apparatus according to claim 3, whereinthe vertical direction detecting optical unit includes a spatial filterfor blocking a diffracted light from a repeated pattern portion formedon the specimen.